Video courses › The basics: saving, inflation, risk › Lesson 3

Compound interest, explained with an example

How compounding works, why time matters more than the rate, and why the same mechanism also works against people in debt.

Video lesson in preparation (AI-generated presenter). Full text below.

Lesson text

When a sum earns interest, one of two things can happen: the interest is withdrawn, or it is left together with the original sum. In the second case, the following year interest is calculated on a larger base, which includes the interest already earned. This mechanism is called compound interest, or compounding.

A hypothetical example helps. Imagine 1,000 euros earning 3% a year, with no costs and no taxes, simply to see the mechanism. After the first year they become 1,030. In the second year the 3% is calculated on 1,030, not on 1,000: the total reaches 1,060.90. The difference from simple interest is 90 cents. It looks like nothing. But after thirty years the sum would be about 2,427 euros, against 1,900 with simple interest.

Two things follow. The first is that time weighs enormously: growth is slow at the start and accelerates later, because each year the base is larger. The second is that the example only works on paper. In reality returns are not constant, can be negative in some years, and costs and taxes must be deducted. A fixed return for thirty years is a calculation assumption, not a forecast.

The same mechanism also works in reverse. On debts, especially those with high rates such as some consumer loans or overdrafts, interest is added to the debt and generates further interest. It works on costs too: a fee that looks small, charged every year for many years, reduces the final result in a compound way. Knowing compound interest therefore helps you read both opportunities and costs more clearly.

In three points

• With compound interest, the interest earned generates interest in turn.
• Time is the factor that weighs most; constant-rate examples are assumptions, not forecasts.
• The mechanism applies to debts and costs as well, which accumulate in the same way.

Educational and informational content only. It is not personalised financial, investment or tax advice. All investments involve risks, including the possible loss of invested capital.

Privacy Policy · Cookie Policy · Terms of Service · Financial Disclaimer · About Us · Contact · Resources · Legal notice (Impressum)